Lenses are commonly used to alter the shape of the illumination/radiation pattern produced by a light source. Elongated illumination patterns are often required for camera flash lamps, vehicle head lamps, street lighting, and so on.
U.S. Pat. No. 7,339,200, “LIGHT-EMITTING DIODE AND VEHICULAR LAMP”, issued 4 Mar. 2008 to Amano et al. discloses a lens that provides an elongated illumination pattern for a vehicular lamp by increasing the divergence of light from a light emitting device along one axis. To compensate for the greater intensity of light when viewed from the center of the light emitting source, compared to the off-center intensity, the lens includes a concave portion about an optical center of the light emitting device, and a convex portion on either side of the optical center, the convex portions having a larger emission surface than the concave portion. The resultant lens is “peanut shaped”, the concave portion corresponding to the narrowed center portion of a peanut shell.
FIGS. 1A-1D illustrate an example peanut shaped lens 100 that provides an elongated illumination pattern from a single light source that emits a Lambertian radiation pattern. FIG. 1A is a perspective view that illustrates the peanut shape having a narrowed center region 110 separating two larger lobes 120. The illustrations are not to scale, and may include exaggerated features for ease of illustration and explanation. In some embodiments, the difference in size/volume between the larger lobes 120 and the smaller center region 110 may be substantially less than illustrated in these figures.
FIG. 1B illustrates a top view of the peanut shaped lens of FIG. 1A, while FIGS. 1C and 1D illustrate cross-section views taken along views C-C and D-D, respectively, of FIG. 1B. The view C-C is taken along the long axis 130, and the view D-D is taken along the short axis 140. As illustrated in FIG. 1C, the larger lobes 120 form a convex surface, and the center region 110 forms a concave structure, as viewed along cross-section C-C. As illustrated in FIG. 1D, the cross-section of the center region 110 forms a convex surface. This convex cross-section extends for the entire length of the lens through the long axis 130 of the lens, include the larger lobes 120, the radius of the convex surface changing accordingly. Light source 150 may be a semiconductor light emitting device (LED), or a plurality of light emitting devices, and may be arranged within a recess of the lens or situated on or near the lower surface of the lens.
FIGS. 2A and 2B illustrate the light propagation through the lens 100 with respect to each axis 130, 140, respectively. As disclosed, the lens 100 includes a concave lens portion 210 and two convex lens portions 220 on either side of the concave lens 210. Each of these lens portions provide an optical axis with respect to the light source 150. The concave lens portion 210 provides optical axis 201, and each of the convex lens portions 220 provides an optical axis 202. Each optical axis 202 extends from the light source 150 through the center of curvature 205 of the convex lens portions 220. The concave lens 210 serves to disperse the light emitted from the light source 150 away from the optical axis 201, forming an elongated light emission pattern along the long axis 130. Each of the convex lenses 220 serve to converge the light toward its respective optical axis 202, which results in an elongated light emission pattern along the long axis 130. By proper selection of the size and curvatures of the lenses 210, 220, a uniformly illuminated elongated light emission pattern may be formed.
The cross section of the lens 100 relative to the short axis 140 forms a convex lens 240. The cross section taken along any point on the long axis 130 forms a similarly shaped convex lens, as indicated by the dashed line 240′, the size being relative to the height and width of the lens 100 along the long axis 130. As illustrated, the convex lens 240 serves to concentrate/collimate the light from the light source 150, forming a relatively narrow light emission pattern along the short axis 140. The convex lens 240′ will similarly concentrate/collimate the light from the light source 150, maintaining a narrower light emission pattern along the short axis 140.
The overall emission pattern formed by the lens 100 is long in one axis, and narrow in the other axis, forming a substantially rectangular, or oval illumination pattern. However, the complex shape of the lens 100 introduces interdependencies between the parameters in each dimension. For example, if a wider illumination pattern is desired relative to the short axis (FIG. 2B), the radius of curvature of the convex lens 240 may need to be decreased. This change of shape of the lens 240 may limit the feasible shapes of the lenses 220. Constraints on the physical size of the lens as well as methods of forming a suitable mold may also limit the shape of the lens.